Electrically operated screw driver

ABSTRACT

This specification discloses an electrically operated screw driver comprising in combination, a tool handle accommodating a compact electric motor therein, a driver shank connected to the electric motor and a clutch mechanism arranged therebetween for transmission of the manual driving power from the tool handle to the driver shank by which a substantial part of the screw fastening operation is carried out automatically by an electric power and an ultimate tightening operation is ensured manually with the same screw driver while confirming the degree of tightness.

Totsu States tet [54] ELECTRICALLY OPERATED SCREW DRIVER [72] Inventor: Katsuyuki Totsu, No. 4-7, 3-chome,

Oshiage, Sumida-ku, Tokyo, Japan [22] Filed: Feb. 25, 1970 [21] Appl. No.: 14,034

[30] Foreign Application Priority Data Aug. 29, 1972 1,169,193 1/1916 Ramelli ..144/32 FOREIGN PATENTS OR APPLICATIONS 905,066 9/ 1962 Great Britain 145/50 E Primary ExaminerDonald R. Schran Att0rney-Oberlin, Maky, Donnelly & Renner [57] ABSTRACT This specification discloses an electrically operated screw driver comprising in combination, a tool handle accommodating a compact electric motor therein, a driver shank connected to the electric motor and a clutch mechanism arranged therebetween for transmission of the manual driving power from the tool handle to the driver shank by which a substantial part of the screw fastening operation is carried out automatically by an electric power and an ultimate tightening operation is ensured manually with the same screw driver while confirming the degree of tightness.

7 Claims, 14 Drawing figures P'A'TENTEDmszs m2 SHEET 1 OF 3 INVENTOR KATSUYUKI TOTSU PATENTEB M1829 I972 SHEET 2 BF 3 FIGA FIG. 70

INVENTOR KATSUYUKI TOTSU INVENTOR KATSUYUKI TOTSU PATENTEDmszs 1912 SHEET 3 0F 3 FIG.8

FIGJO BACKGROUND OF THE INVENTION The present invention is concerned with an electrically operated screw driver comprising in combination a tool handle accommodating a compact electric motor therein, a driver shank and a clutch mechanism arranged therebetween for transmission of the manual driving power from the tool handle to the driver shank.

Generally, the driving operation of the screw into the objective threaded hole by means of the screw driver is comprised of the following two steps:

1. A step of standing the screw in the threaded hole and fastening the same under the negligible resistance until the bottom face of the screw head comes into contact with the entry of the threaded hole.

2. An ultimate step of tightening the screw under the increasing resistance.

From the foregoing analysis, it will be appreciated that the first fastening step or the substantial part of the screw fastening is conducted under the light resistance with a relatively extended screwing motion. On the contrary, the ultimate tightening of the screw is conducted under the increasing resistance with the negligible turning motion but with a great driving power.

Heretofore, various types of automatically operated screw drivers by compressed air or electric power have been developed and offered into practical use. However, all of those conventional screw drivers are designed under the common conception to accomplish the whole fastening operation including the final tightening by the compressed air or the electric power with a strong power supply source. For this purpose, the screw driver of air pressure type requires a hose of large dimension and weight for feeding the pressurized air while the screw driver of the electrically driven type is usually provided with a powerful motor of large volume and weight.

Both types, therefore, are not suitable for fastening of the machine screws in the precision working because of their inconveniences and difficulties in operation with undesired noise and danger as well as the possibility of damaging the screw head due to the excessive tightness. After the fastening, even by the screw drivers with the powerful energy supply source, it still remains necessary to confirm the tightening degree of the screw by means of the operators finger feeling relying upon another manually operated screw driver.

Further, the initial standing operation of the screw, especially, machine screws in the threaded hole and, more particularly, the threaded hole located in the retired position is usually cumbersome for the operator, and the greater part of the screw fastening operation is consumed for this initial screw standing operatron.

After extensive research and studies to overcome the above inconveniences and difficulties, the inventor has succeeded in providing a new electrically operated screw driver particularly suitable for driving the machine screws in the precision working by which the substantial part of the screw fastening is carried out automatically by the electric power without encountering difficulty in standing the screw in the threaded hole, and the ultimate tightening is accomplished by a slight manual operation while confirming the degree of tightness under a quick conversion from the electrical operation to the manual operation without necessitating any special converter.

SUMMARY OF THE INVENTION With the foregoing in mind, the general object of the invention is to provide an electrically operated screw driver which effectuates a substantial part of the screw fastening automatically by the actuation of the electric power and ensures the ultimate tightening manually while confirming the degree of tightness under the quick driving motion.

The principal object of the invention is to provide an electrically operated screw driver comprising a tool handle accommodating a compact electric motor therein, a driver shank and a clutch mechanism arranged therebetween for transmission of the manual driving power from the tool handle to the driver shank in which an electrical driving power is transmitted from the electric motor to the driver shank directly whereas the manual driving power is transmitted from the tool handle through the clutch mechanism to the driver shank.

Another object of the invention is to provide an electrically operated screw driver comprising a tool handle accommodating a compact electric motor therein, a driver shank, a clutch mechanism arranged therebetween for transmission of the manual driving power from the tool handle to the driver shank, and a releasing mechanism mounted around the driver shaft in abutment with the clutch mechanism for idling the tool handle when the tightness of the screw gets over a certain limit, in which the electrical driving power is transmitted from the electric motor to the driver shank directly whereas the manual driving power is transmitted from the tool handle through the clutch mechanism and the release mechanism to the driver shaft.

A further object of the invention is to provide an electrically operated screw driver which comprises a tool handle accommodating a compact electric motor therein, a driver shank which is provided with a screw holding means and a clutch mechanism arranged therebetween for transmission of the manual driving power from the tool handle to the driver shank.

Yet, a further object of the invention is to provide an electrically operated screw driver which comprises a tool handle accommodating a compact electric motor therein, a driver shank which is provided with a screw holding means, a clutch mechanism for transmission of the manual driving power from the tool handle to the driver shank and a releasing mechanism mounted around the driver shaft in abutment with the clutch mechanism for idling the tool handle when the tightness of the screw gets over a certain limit Still a further object of the invention is to provide a combination of aforementioned electrically operated screw driver with a screw which at its head portion is provided with a screw slot with a central hole of greater diameter and depth than the width and depth of the slot.

These and other objects and advantages of the invention will become apparent as the description proceeds in particular reference to the appended drawings, in which:

3 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation of the electrically operated screw driver according to the invention;

FIG. 2 is a fragmentarily and longitudinally sectioned view ofFIG. 1;

FIG. 3 is a pictorial view depicting the state in tightening operation of the screw driver of FIG. 1;

FIG. 4 is a front elevation of the electrically operated screw driver of another embodiment according to the invention;

FIG. 5 is a fragmentarily and longitudinally sectioned view of FIG. 4;

FIGS. 60 to c are pictorial views of the release mechanism before assembly;

FIGS. 70 and b are pictorial views of the release mechanism before assembly of another embodiment;

FIG. 8 is a perspective view, fragmentarily enlarged, of the screw holding means according to the invention;

FIG. 9 is a perspective view, partially recessed, of the screw suitable for the screw driver of the invention;

FIG. 10 is a pictorial view illustrating the screw holding means suspending the screw; and

FIG. I 1 is a plan view of the screw the line AA of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION Referring now in more detail to the drawings, wherein like parts are indicated by like reference numerals, and initially to FIGS. I and 2, there is illustrated therein in front and longitudinally sectioned views a tool handle of the screwdriver 10 which is comprised of an outer sleeve 12 and a flanged cover 14 secured thereto in which a compact electric motor 16 is accommodated. A driven shaft 18 extending from the electric motor 16 is connected to an intermediate shaft 20 which is in turn coupled releasably at its other end with a driver shank 22. The intermediate shaft 20 at its lower end is provided with an insertion bore 24 and a diametric recess 26.

The driver shank 22 at its upper end portion is provided with a diametric slot 28 and two symmetrically and outwardly extending projections 30 adapted to fit into the diametric recess 26 for transmitting the rotation of the intermediate shaft 20 to the driver shank 22. In the coupling of the driver shank 22 with the intermediate shaft 20, the slotted end of the driver shank is forced into the insertion bore 24 of the intermediate shaft 20 so that the driver shank 22 is rigidly associated with the intermediate shaft 20 under the resilient influence of the legs on either side of the slot 28.

It will be appreciated that the intermediate shaft 20 and the driver shank 22 may be formed integrally as a single driver shank without providing complicated coupling construction.

As best shown in FIG. 2, the flanged cover 14 is provided with an extended constriction 32 and a ring 34 of the same outer diameter as the extended constriction 32 is mounted around the outer circumference of the intermediate shaft 20 in abutment with the said extended constriction 32 by a suitable fastener. Around the outer circumference of the extended constriction 32 and the ring 34 is mounted a grip coil 36 for ensuring the transmission of one way rotation of the tool handle it) to the driver shank 22.

head taken along In the operation, a push button switch 38 mounted on the top end of the tool handle 10 is pushed downwardly by a finger of the operator to actuate the electric motor 16. The rotation of the driven shaft 18 is transmitted through the intermediate shaft 20 to the driver shank 22 and thus the substantial part of the fastening operation of the screw is accomplished in an instant by the actuation of the electric motor. In that case, the intermediate shaft 20 and the ring 34 affixed thereto turn in the counter direction to the spiral direction of the grip coil 36 so that a smooth rotation of both members is attained without being subjected to any frictional influence of the grip coil 36.

When the fastening operation carried out by the electric power comes to the ultimate tightening step, the rotation of the driver shank is decreased abruptly due to the resistance of the screw and at last the driving motion is ceased.

Then, the tool handle 16 is intentionally turned by manual operation in a clockwise direction so that the manual driving power is transmitted from the extended constriction 32 of the flanged cover 14 through the grip coil 36 to the ring 34 for turning of the driver shank 22. In that case, the turning direction of the extended constriction 32 is coincident with the spiral direction of the grip coil 36 mounted therearound and consequently by the turning of the extended constriction, the grip coil 36 is tightened firmly to transmit the turning motion to the ring 34 under the principle of the coil-grip friction clutch mechanism.

Thus, the ultimate tightening operation may be manually carried out in a positive way while confirming the degree of tightness by the finger feeling as seen in FIG. 3. It will be appreciated that the electrically operated screw driver according to the invention may also be driven without necessitating any electric power supply source.

As best shown in FIGS. 4 and 5, there is provided a release mechanism for releasing the excessive tightness of the screw to be caused by the manual driving operation.

According to this embodiment, the ring 34 is free from the intermediate shaft 20 but is provided at its bottom face with a ridge 40 adapted to fit into a plurality of feed recesses 44 provided in a cam ring 42 having a keyway 46 into which a key or pin 48 is inserted through the intermediate shaft 20 to retain the cam ring 42 at the lower end of the intermediate shaft 20 as seen in FIGS. 4, 5 and 6.

Beneath the cam ring 42 is arranged a spring 50 for the resilient support of the cam ring 42 and this spring 50 is carried by a nut 52 mounted vertically adjustably along the threaded end of the intermediate shaft 20 to provide an allowable limit of the tightness of the screw. That is, the co-acting effect of the ridge 40 with the recess M is increased with an elevation of the location of the nut 52 for compression of the spring 5t thereby enhancing the allowable limit of the tightness of the screw.

On the other hand, when the adjusting nut 52 is located in a lower position, the spring 50 is relatively relaxed. In consequence, when the manual driving power gets over the allowable limit, the cam ring 42 is frictionally stressed downwardly even with a relatively low tightening power so that the tool handle 10 with the ring 34 is subjected to lost motion. Thus, the ultimate tightening of the screw in relatively soft material such as a base plate of synthetic resin may be accomplished without injuring the screw or the base plate.

Further, in order to attain a quick release of the excessive tightening against the screw, the ring 34 at its bottom face may be provided with a plurality of steel balls 54 in lieu of the ridge 40 as best shown in FIG. 7.

In both of the foregoing embodiments, the electric driving power may be increased by providing a suitable reduction gear mechanism such as a planetary reduction gear between the driving shaft and the driven shaft.

in FIGS. 8 and 10, the screw holding means according to the invention comprises a shank end 56 provided with a diametric slot 58 and a center bore 60 of greater diameter and depth than the width and depth of the diametric slot 58, a replaceable driver bit 62 of rigid material having suitable size and thickness to fit into the diametric slot 58 and a resilient screw holding member 64 inserted into the center bore 60 so that a limited clearance is formed between the driving bit 62 and the screw holding member 64 so that the screw is resiliently retained by the screw holding means, as will be presently described.

The driver bit 62 at its edge portion is further provided with a center projection 66 adapted to facilitate the fitting of the driver bit 62 into the screw slot and the end of the screw holding member 64 is extended to coincide with the top end of the projection 66.

The screw holding means of the above construction is most suitable in driving a screw 68 having a screw slot 70 with a central hole 72 of greater diameter and depth than the width and depth of the slot 70 as best shown in FIG. 9. As seen in FIGS. and 11, when the blade is inserted into the screw slot the screw holding member 64 is in tight resilient contact with the wall of the center hole 72 of the screw while the opposite side of the bit 62 is thrust against the side wall of the screw slot 70 thereby ensuring holding of the screw for the subsequent driving operation without difficulty in standing the screw into the threaded hole. Thus, the screw driving operation, particularly the first fastening operation, is greatly facilitated.

It will thus be seen that the electrically operated screw driver according to the invention is operationally effective in driving the machine screws and the compact electric motor is sufiicient as a power supply source since the ultimate tightening operation is carried out manually.

While certain preferred embodiments of the invention have been illustrated by way of example in the drawings and particularly described, it will be un mechagism, said clutch mechanism being Q eratively couple to said release mechanism, sax release mechanism being uncoupled from said clutch mechanism for idling said tool handle when the manual tightening of the screw by said tool handle has exceeded a permissible limit thereby to prevent damage to the screw or the material to which the screw is mounted.

2. The electrically operated screw driver of claim 1,

wherein said release mechanism comprises a clutch ring provided at its bottom end with projection means, said clutch ring being mounted around but free from said driver shank, a cam ring mounted around said shank adjacent said clutch ring, said cam ring being keyed to said shank for rotation therewith and limited vertical movement relative thereto, said cam ring being provided at its end adjacent said clutch ring with a plurality of recesses for mating engagement with said projection means, a spring mounted around said driver shank to support said cam ring, and a nut mounted vertically adjustably along the threaded end of said driver shank to firmly bear against said spring.

3. The electrically operated screw driver of claim 2, wherein said projection means comprises a pair of ridges.

4. The electrically operated screw driver of claim 2, wherein said projection means comprises a plurality of balls.

5. The electrically operated screw driver of claim I, wherein said driver shank is provided with a driver bit with a center projection and a resilient screw holding member.

6. The electrically operated screw driver of claim 5 in combination with a screw which is provided with a screw slot and a central hole of greater diameter and depth than the width and depth of said slot.

7. The electrically operated screw driver of claim 1, wherein said clutch mechanism comprises a coil-grip friction clutch. 

1. An electrically operated screw driver comprising a tool handle accommodating an electric motor therein, a driver shank directly connected to said motor for rotation thereby, a clutch mechanism positioned around said shank and a portion of said tool handle for transferring manual rotation of said tool handle to said shank for final tightening of said screw, a release mechanism between said shank and said clutch mechanism, said clutch mechanism being operatively coupled to said release mechanism, said release mechanism being uncoupled from said clutch mechanism for idling said tool handle when the manual tightening of the screw by said tool handle has exceeded a permissible limit thereby to prevent damage to the screw or the material to which the screw is mounted.
 2. The electrically operated screw driver of claim 1, wherein said release mechanism comprises a clutch ring provided at its bottom end with projection means, said clutch ring being mounted around but free from said driver shank, a cam ring mounted around said shank adjacent said clutch ring, said cam ring being keyed to said shank for rotation therewith and limited vertical movement relative thereto, said cam ring being provided at its end adjacent said clutch ring with a plurality of recesses for mating engagement with said projection means, a spring mounted around said driver shank to support said cam ring, and a nut mounted vertically adjustably along the threaded end of said driver shank to firmly bear against said spring.
 3. The electrically operated screw driver of claim 2, wherein said projection means comprises a pair of ridges.
 4. The electrically operated screw driver of claim 2, wherein said projection means comprises a plurality of balls.
 5. The electrically operated screw driver of claim 1, wherein said driver shank is provided with a driver bit with a center projection and a resilient screw holding member.
 6. The electrically operated screw driver of claim 5 in combination with a screw which is provided with a screw slot and a central hole of greater diameter and depth than the width and depth of said slot.
 7. The electrically operated screw driver of claim 1, wherein said clutch mechanism comprises a coil-grip friction clutch. 